U.S. patent number 4,507,173 [Application Number 06/421,294] was granted by the patent office on 1985-03-26 for pattern bonding and creping of fibrous products.
This patent grant is currently assigned to James River-Norwalk, Inc.. Invention is credited to Bernard G. Klowak, Nilo I. Salmeen, Jr., deceased.
United States Patent |
4,507,173 |
Klowak , et al. |
March 26, 1985 |
Pattern bonding and creping of fibrous products
Abstract
A web (12) of highly bulked substrate is passed into a nip
formed between a gravure roller (14) and an impression roller (15).
The impression roller has raised areas defining an interconnected
network of lines such that the web is compressed only under the
raised areas; as a result, the binding liquid applied by the
gravure roller (14) to the web is absorbed substantially through
the web in the compressed areas. The gravure roller (14) may have a
uniform surface, such that a light coating of binding liquid is
applied to the surface of the uncompressed areas in the web, or the
gravure roller may have a pattern of etched grooves or cells which
matches and registers with the pattern of raised areas on the
impression roller. In the latter embodiment, binding liquid will be
absorbed into the web only in the compressed areas. The coated web
(21) is applied to the surface (24) of a creping cylinder (25), is
dried thereon, and is creped off with a creping blade (27) to form
a product bound together by an interconnected network of lines of
strength extending through the web. The areas between the lines of
strength are not compressed and are not substantially coated with
binding liquid, and thereby retain high bulk and absorbency. The
once creped web may be passed through the identical process a
second time such that the other side of the web receives binding
liquid. The twice coated product still retains high bulk and
absorbency in those areas which have not been compressed, and has
lines of strength extending in a network through the product where
the binding liquid has been applied. In a modified embodiment of
the invention, a single impression/pressure roller with raised
areas thereon is presses the web against a gravure roller and
applies the web to a creping cylinder; and in a second modified
embodiment, the web is pressed and coated on one side, is
substantially hot air dried without compression, is coated with
binding liquid applied to the other side, and is then applied to
and creped from a creping cylinder.
Inventors: |
Klowak; Bernard G. (Neenah,
WI), Salmeen, Jr., deceased; Nilo I. (late of Neenah,
WI) |
Assignee: |
James River-Norwalk, Inc.
(Norwalk, CT)
|
Family
ID: |
26878470 |
Appl.
No.: |
06/421,294 |
Filed: |
September 22, 1982 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
182834 |
Aug 29, 1980 |
|
|
|
|
Current U.S.
Class: |
162/112; 156/183;
162/113; 264/283 |
Current CPC
Class: |
B31F
1/12 (20130101); D21H 23/58 (20130101); D21H
5/0032 (20130101); D21F 11/006 (20130101) |
Current International
Class: |
B31F
1/00 (20060101); B31F 1/12 (20060101); D21F
11/00 (20060101); D21H 005/24 () |
Field of
Search: |
;162/111,112,113,134,135,136,137,117 ;156/183,62.2,209,291
;264/283,128,121,282 ;427/264,275,288,271,361,428,356 ;428/154 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chin; Peter
Attorney, Agent or Firm: Isaksen, Lathrop, Esch, Hart &
Clark
Parent Case Text
This application is a continuation in part of prior application
Ser. No. 182,834, filed Aug. 29, 1980 now abandoned.
Claims
We claim:
1. A process for bonding and enhancing the bulk of a highly bulked
low strength fibrous web, comprising the steps of:
(a) passing a highly bulked, low strength fibrous substrate web,
which has low internal fiber bonding such that creping of the
substrate will tend to separate and fluff up the fibers, into a nip
between a gravure roller and an impression roller, the impression
roller having a resilient surface with raised areas defining an
interconnected network and depressed areas between the raised areas
such that the web is compressed under the raised areas of the
impression roller and the remainder of the web is left
substantially uncompressed, the height of the raised areas above
the depressed areas selected to be greater than the uncompressed
thickness of the substrate web, the gravure roller having
depressions which carry binding liquid in a pattern which underlies
and registers with the raised areas on the impression roller such
that binding liquid is absorbed substantially through the
compressed areas of the web while the other areas of the web
receive substantially no binding liquid;
(b) applying the web to a heated, moving creping surface with a
pressure roller having raised areas and depressed areas to define a
pattern therein, the height of the raised areas above the depressed
areas selected to be greater than the uncompressed thickness of the
substrate web, the web being compressed only by the raised areas of
the pressure roller with the binding liquid coated side of the web
against the creping surface to cause the web to adhere thereto with
the binding liquid; and
(c) creping the web by removing it from the creping surface with a
creping blade such that the bulk of the web so creped is greater
than the bulk of the substrate web.
2. A process for bonding and enhancing the bulk of a highly bulked,
low strength fibrous substrate web, comprising the steps of:
(a) passing a highly bulked, low strength fibrous substrate web,
which has low internal fiber bonding such that creping of the
substrate will tend to separate and fluff up the fibers, into a nip
between a gravure roller and an impression roller, the gravure
roller providing binding liquid on its surface to one side of the
web, and the impression roller having a resilient surface with
raised areas defining an interconnected network and depressed areas
between the raised areas such that the web is compressed under the
raised areas of the impression roller and the remainder of the web
is left substantially uncompressed, the height of the raised areas
above the depressed areas selected to be greater than the
uncompressed thickness of the substrate web, the binding liquid on
the surface of the gravure roller being absorbed substantially
through the compressed areas of the web;
(b) applying the web to a heated, moving creping surface with a
pressure roller having raised areas and depressed areas to define a
pattern therein, the height of the raised areas above the depressed
areas selected to be greater than the uncompressed thickness of the
substrate web, the web being compressed only by the raised areas of
the pressure roller with the binding liquid coated side of the web
against the creping surface to cause the web to adhere thereto with
the binding liquid; and
(c) creping the web by removing it from the creping surface with a
creping blade such that the bulk of the web so creped is greater
than the bulk of the substrate web.
3. A process for bonding and enhancing the bulk of a highly bulked,
low strength fibrous substrate web, comprising the steps of:
(a) passing a highly bulked, low strength fibrous substrate web,
which has low internal fiber bonding such that creping of the
substrate will tend to separate and fluff up the fibers, into a nip
between a gravure roller and an impression roller, the gravure
roller providing binding liquid on its surface to one side of the
web, and the impression roller having a resilient surface with
raised areas defining an interconnected network and depressed areas
between the raised areas such that the web is compressed under the
raised areas of the impression roller and the remainder of the web
is left substantially uncompressed, the height of the raised areas
above the depressed areas selected to be greater than the
uncompressed thickness of the substrate web, the binding liquid on
the surface of the gravure roller being absorbed substantially
through the compressed areas of the web;
(b) rotating the impression roller and maintaining the compressed
and uncompressed areas of the web in respective registry with the
raised and depressed areas on the impression roller as it
rotates;
(c) passing the web on the impression roller into a nip formed
between the impression roller and a moving, heated creping surface
such that the raised areas of the impression roller press the once
compressed areas of the web against the creping surface to adhere
the web thereto with the binding liquid; and
(d) creping the web by removing it from the creping surface with a
creping blade such that the bulk of the web so creped is greater
than the bulk of the substrate web.
4. A process for bonding and enhancing the bulk of a highly bulked,
low strength fibrous substrate web, comprising the steps of:
(a) passing a highly bulked, low strength fibrous substrate web,
which has low internal fiber bonding such that creping of the
substrate will tend to separate and fluff up the fibers, into a nip
between a gravure roller and an impression roller, the gravure
roller providing binding liquid on its surface to one side of the
web, and the impression roller having a resilient surface with
raised areas defining an interconnected network and depressed areas
between the raised areas such that the web is compressed under the
raised areas of the impression roller and the remainder of the web
is left substantially uncompressed, the height of the raised areas
above the depressed areas selected to be greater than the
uncompressed thickness of the substrate web, the binding liquid on
the surface of the gravure roller being absorbed substantially
through the compressed areas of the web;
(b) passing heated air through the binding liquid coated web to
substantially dry it;
(c) passing the dried web into a nip formed between a gravure
roller and an impression roller, the gravure roller providing
binding liquid on its surface to the side of the web opposite that
to which binding liquid had previously been applied, and the
impression roller having raised areas defining an interconnected
network and depressed areas between the raised areas such that the
web is compressed under the raised areas of the impression roller
and the remainder of the web is left substantially uncompressed by
the impression roller, the height of the raised areas above the
depressed areas selected to be greater than the uncompressed
thickness of the substrate web, the binding liquid on the surface
of the gravure roller being absorbed substantially through the
compressed areas of the web;
(d) applying the web to a heated, moving creping surface with a
pressure roller having raised areas and depressed areas to define a
pattern therein, the height of the raised areas above the depressed
areas selected to be greater than the uncompressed thickness of the
substrate web, the web being compressed only by the raised areas of
the pressure roller with the binding liquid coated side of the web
against the creping surface to cause the web to adhere thereto with
the binding liquid; and
(e) creping the web by removing it from the creping surface with a
creping blade such that the bulk of the web so creped is greater
than the bulk of the substrate web.
5. A process for bonding and enhancing the bulk of a highly bulked,
low strength fibrous substrate web, comprising the steps of:
(a) passing a highly bulked, low strength fibrous substrate web,
which has low internal fiber bonding such that creping of the
substrate will tend to separate and fluff up the fibers, into a nip
between a gravure roller and an impression roller, the gravure
roller providing binding liquid on its surface to one side of the
web, and the impression roller having a resilient surface with
raised areas defining an interconnected network and depressed areas
between the raised areas such that the web is compressed under the
raised areas of the impression roller and the remainder of the web
is left substantially uncompressed, the height of the raised areas
above the depressed areas selected to be greater than the
uncompressed thickness of the substrate web, the binding liquid on
the surface of the gravure roller being absorbed substantially
through the compressed areas of the web;
(b) applying the web to a heated, moving creping surface with
pressure applied by a pressure roller having raised areas and
depressed areas to define a pattern therein, the height of the
raised areas above the depressed areas selected to be greater than
the uncompressed thickness of the substrate web, the web being
compressed only by the raised areas of the pressure roller with the
binding liquid coated side of the web against the creping surface
to cause the web to adhere thereto with the binding liquid;
(c) creping the web by removing it from the creping surface with a
creping blade;
(d) passing the creped web into a nip between a second gravure
roller and a second impression roller, the second gravure roller
providing binding liquid on its surface to the side of the web
opposite that to which binding liquid had previously been applied,
and the second impression roller having a resilient surface with
raised areas defining an interconnected network and depressed areas
between the raised areas such that the web is compressed under the
raised areas of the second impression roller and the remainder of
the web is left substantially uncompressed by the second impression
roller, the height of the raised areas above the depressed areas
selected to be greater than the uncompressed thickness of the
substrate web, the binding liquid on the surface of the second
gravure roller being absorbed substantially through the areas of
the web compressed by the second impression roller;
(e) applying the web to a heated, moving creping surface with
pressure applied by a pressure roller having raised areas and
depressed areas to define a pattern therein, the height of the
raised areas above the depressed areas selected to be greater than
the uncompressed thickness of the substrate web, the web being
compressed only by the raised areas of the pressure roller with the
binding liquid coated side of web against the creping surface to
cause the web to adhere thereto with the binding liquid; and
(f) creping the web by removing it from the creping surface with a
creping blade, such that the bulk of the web so creped is greater
than the bulk of the substrate web.
6. A process for bonding and enhancing the bulk of a highly bulked,
low strength fibrous substrate web, comprising the steps of:
(a) passing a highly bulked, low strength fibrous substrate web,
which has low internal fiber bonding such that creping of the
substrate will tend to separate and fluff up the fibers, into a nip
between a gravure roller and an impression roller, the gravure
roller providing binding liquid on its surface to one side of the
web, and the impression roller having a resilient surface with
raised areas defining an interconnected network and depressed areas
between the raised areas such that the web is compressed under the
raised areas of the impression roller and the remainder of the web
is left substantially uncompressed, the height of the raised areas
above the depressed areas selected to be greater than the
uncompressed thickness of the substrate web, the binding liquid on
the surface of the gravure roller being absorbed substantially
through the compressed areas of the web;
(b) rotating the impression roller and maintaining the compressed
and uncompressed areas of the web in respective registry with the
raised and depressed areas on the impression roller as it
rotates;
(c) passing the web on the impression roller into a nip formed
between the impression roller and moving, heated creping surface
such that the raised areas of the impression roller press the once
compressed areas of the web against the creping surface to adhere
the web thereto with the binding liquid;
(d) creping the web by removing it from the creping surface with a
creping blade;
(e) passing the creped web into a nip between a second gravure
roller and a second impression roller, the second gravure roller
providing binding liquid on its surface to the side of the web
opposite that to which binding liquid had previously been applied,
and the second impression roller having a resilient surface with
raised areas defining an interconnected network and depressed areas
between the raised areas such that the web is compressed under the
raised areas of the second impression roller and the remainder of
the web is left substantially uncompressed by the second impression
roller, the height of the raised areas above the depressed areas
selected to be greater than the uncompressed thickness of the
substrate web, the binding liquid on the surface of the second
gravure roller being absorbed substantially through the areas of
the web compressed by the second impression roller;
(f) rotating the second impression roller and maintaining the
compressed and uncompressed areas of the web in respective registry
with the raised and depressed areas on the second impression roller
as it rotates;
(g) passing the web on the second impression roller into a nip
formed between the second impression roller and a moving, heated
creping surface such that the raised areas of the second impression
roller press the once compressed areas of the web against the
creping surface to adhere the web thereto with the binding liquid;
and
(h) creping the web by removing it from the creping surface with a
creping blade such that the bulk of the web so creped is greater
than the bulk of the substrate web.
7. The process of claim 2, 3 or 4 wherein the raised area of the
impression roller is between 20% and 40% of the total area of the
surface of the roller.
8. The process of claim 1, 2, 3 or 4 wherein the binding liquid is
capable of being cured to a hardened and insoluble state, and
further including the step of curing the binding liquid in the
creped web to thereby provide lines of strength in the web
corresponding to the interconnected networks of cured binding
liquid in the web.
9. The process of claim 5 or 6 wherein the binding liquid is
capable of being cured to a hardened and insoluble state, and
further including the step of curing the binding liquid in the
creped web to thereby provide lines of strength in the web
corresponding to the interconnected networks of cured binding
liquid in the web.
10. The process of claim 8 wherein the binding liquid is heat
curable, and wherein the step of curing the binding liquid
comprises applying hot air to the creped web for a time sufficient
to cure the binding liquid.
11. The process of claim 10 wherein the binding liquid includes a
mixture of ethylene vinyl acetate polymer and acrylic polymer.
12. The process of claim 9 wherein the binding liquid is heat
curable to a hardened and insoluble state, and wherein the step of
curing the binder liquid comprises applying hot air to the creped
web for a time sufficient to cure the binding liquid.
13. The process of claim 12 wherein the binding liquid includes a
mixture of ethylene vinyl acetate polymer and acrylic polymer.
14. The process of claim 2, 3 or 4 wherein the raised areas on the
impression roller define a rectilinear network pattern which
surround depressed areas having a quadrangular shape.
15. The process of claim 1 wherein the interconnected network of
areas compressed in the web defines a rectilinear network
pattern.
16. The process of claim 1 wherein the step of applying the web to
the creping surface includes passing the web having a coating of
binding liquid thereon into a nip between a pressure roller and the
moving creping surface.
17. The process of claim 16 wherein the pressure roller has raised
areas and depressed areas to define a pattern therein, with the web
being compressed by the raised areas of the pressure roller.
18. The process of claim 2, 3, 4, 5 or 6 in which each gravure
roller has a uniform surface composed of cells acting as reservoirs
for binding liquid, the binding liquid being absorbed substantially
through the areas of the web which are compressed against each
gravure roller, and coated on the surface of the areas of the web
which are not so compressed.
19. The process of claim 2, 3, 4, 5 or 6 in which each gravure
roller has depressions on its surface acting as reservoirs for
binding liquid and arranged in a pattern which matches and
registers with the raised areas of the impression roller which
presses the web against the gravure roller, the areas of the
gravure roller between the pattern areas being smooth so as not to
pick up binding liquid, such that the binding liquid is
substantially absorbed through those areas of the web which are
compressed against the gravure roller while the remainder of the
web receives no binding liquid from the gravure roller.
Description
TECHNICAL FIELD
This invention relates generally to the field of paper making and
converting, and particularly to processes and apparatus for bonding
low strength webs to form products suitable for use as towels and
tissues.
BACKGROUND ART
Paper products that are used for toweling and some types of tissues
have several preferred but sometimes conflicting characteristics.
For example, the products should have good bulk, a soft feel, and
high absorbency of both water and oily liquids; yet the products
should also have good tensile strength even while wet and
resistance to "linting" of fibers from the toweling when rubbed.
Processes that have aimed at achieving these objectives usually
have utilized an initial substrate web of fibers which is formed
with low internal bonding, such as is obtained from air laying or
through-air-drying paper making processes, and have applied a wet
strength binder to one or both sides of the web to provide the
necessary tensile strength and resistance to linting. The liquid
binder is customarily applied by passing the web through a nip
between a gravure roller, which picks up the liquid binder, and a
back-up or impression roller. Because of the pressure placed on the
web at this nip and the migration of the binding liquid through the
fibers of the web, the application of adhesive in this manner tends
to result in an overall compaction and strengthening of the
web.
One approach to reducing the strengthening effect is the use of a
patterned gravure roller, as shown, e.g., in the U.S. patent to
Roberts, Jr. U.S. Pat. No. 4,000,237, in which binding liquid is
applied to the web over only a portion of the web surface. In this
type of process, the web with binding liquid thereon is applied to
a creping cylinder--with the binder acting as a creping
adhesive--and is creped off to yield a product having a creping
pattern which generally matches the pattern of binding liquid
application. An overall compaction of the web still takes place at
the nip between the gravure and back-up rollers and at the nip
formed between the pressure roller and the surface of the creping
cylinder.
Creping patterns may also be formed in the web by utilizing a
patterned roller which presses an adhesive coated web against the
creping cylinder, as shown in the U.S. patent to Klowak, et al.,
U.S. Pat. No. 4,125,659. The application of creping liquid to the
web is uniform, and any additional strenthening of the web results
only from the compaction of the web under the patterned roller.
DISCLOSURE OF THE INVENTION
The product of the present invention is a single ply tissue or
towel type product formed from an initial substrate which has high
bulk and absorbency but which requires the addition of a binder in
it to give it the required tensile strength. The desired level of
tensile strength and bonding is provided by an interconnected
network of areas in the product which have a high concentration of
binder in them and which are highly compressed. Substantial areas
of the product are left uncompressed and highly bulked with very
little binder in them except for a light coating at the surface if
desired to inhibit linting of fibers; these highly bulked areas
serve to provide exceptional liquid absorbency for the product as a
whole. The finished product thus combines the desirable properties
of high tensile strength, resistance to linting at the surfaces if
a surface coating of binder is applied, a soft, bulky feel as
perceived by the consumer, and excellent absorbency.
In a process of the invention, a dry web of highly bulked substrate
is passed into a nip formed between a gravure roller and a back-up
or impression roller. The gravure roller may have a uniform pattern
of engraved lines on its surface to pick up the binding liquid and
apply it in a uniform pattern on one surface of the web. The
impression roller has raised areas defining an interconnected
network which press the portions of the web under the raised areas
firmly against the surface of the gravure roller, while the
isolated areas of the impression roller between the raised areas
are depressed a distance greater than the thickness of the
substrate web and thus leave the areas of the web thereunder
substantially uncompressed. The pressure applied by the raised
surfaces causes binding liquid to be dispersed deeply into the
compressed areas of the web while the uncompressed areas receive a
very light coating of binder which does not penetrate substantially
beyond the surface fibers. The compressed areas are thus greatly
strengthened because of increased hydrogen bonding naturally
occurring between the compacted fibers and because of the
concentration of binder in the fibers which is insolubilized after
curing.
After pickup of the binding liquid, the web is applied to the
surface of a heated drier cylinder for drying, and is then creped
off with a creping blade. The binding liquid on the surface of the
web also serves as a creping adhesive, providing sufficient
adhesion between the web and the drier surface to allow the desired
creping action at the creping blade. The creping of the web tends
to separate and fluff up the fibers in the uncompressed areas.
The web laminate may be passed through the identical process once
again, with the binding liquid being applied this time to the
opposite surface of the web; the web is then applied to another
drier cylinder, creped off, calendered if desired, hot air
flotation dried to cure the binder, and rewound for later use.
It is generally desirable to avoid overall compaction of the web
during the aforementioned processing steps. Where a pressure roller
is used to apply the web firmly against the drier surface, the
pressure roller preferably also has raised surfaces defining an
interconnected network which leaves depressed areas which do not
compress the web. In this manner, even though portions of the web
will be very firmly compressed during processing, a substantial
area of the web will have undergone very little or no compression
and will therefore allow the overall finished product to retain the
desired characteristics of softness, bulk and absorbency.
In an alternative preferred embodiment, the percentage of the area
of the web that is compressed may be reduced further by utilizing a
combination impression/pressure roller, mounted against the drier
cylinder, which has a raised pattern on its surface and which also
acts as the back-up roller for the gravure roller that applies the
binding liquid to the web. The web is fed into the nip formed
between the impression roller and the gravure roller, and the areas
of the web that are compressed by the raised areas on the
impression roller remain in registry with these raised areas as the
roller rotates into contact with the surface of the drier. The
once-pressed areas of the web are pressed again at the nip between
the impression/pressure roller and the drier cylinder, and the
areas of the web between the raised areas on the roller are never
compressed at all since they always remain in registry with the
depressed areas on the roller. The interconnected network of
compressed areas in the web provides tensile strength to the web as
a whole, and the binding liquid may be applied over the entire
surface of the web to act as a creping adhesive on the drier. After
the first creping, the web may be passed through the process again
with the other side of the web having binding liquid applied
thereto.
The process of the invention may also be carried out by eliminating
the first creping step and replacing it with the step of passing
the web, with binding liquid on one surface, through an air
flotation drier to dry the web without pressing it. The drying step
may also be performed by applying the web to a drying cylinder
without pressing. After the binding liquid has been dried on the
one surface of the web, the web is passed through a second gravure
station to apply binding liquid to its other surface, in the manner
described above, and is then transferred to a heated drier cylinder
from which it is creped.
The process as described above may utilize application of binding
liquid to one side of the web from a uniformly engraved gravure
roller, so that binding liquid is absorbed deeply into the product
where it is compressed by the raised areas on the impression roller
while the remainder of the product receives a light, surface
coating of binding liquid. Alternatively, the gravure roller may
have a recessed pattern of grooves, cells or engraved lines which
underlies and registers with the raised area pattern on the
impression roller so that binding liquid is absorbed into the
product in a pattern. Thus, surface areas of the product between
the pressed pattern areas would be free of binding liquid.
Further objects, features and advantages of the invention will be
apparent from the following detailed description taken in
conjunction with the accompanying drawings showing preferred
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a somewhat simplified schematic view of a continuous web
bonding and creping apparatus in accordance with the invention.
FIG. 2 is a stylized isometric view of a pressure for impression
roller in accordance with the invention having raised surfaces
defining an interconnecting rectilinear network.
FIG. 3 is a simplified schematic view of an alternative embodiment
of a continuous web bonding and creping apparatus in accordance
with the invention.
FIG. 4 is a more detailed view of the application of binding liquid
to the web in the apparatus of FIG. 3.
FIG. 5 is a more detailed view of the application of binding liquid
to the web as accomplished in the apparatus of FIG. 1 or the
apparatus of FIG. 6.
FIG. 6 is a schematic view of another alternative embodiment of
continuous web bonding and creping apparatus in accordance with the
invention.
FIG. 7 is an illustrative view of the application of binding liquid
to the web in which the gravure roller has a pattern therein which
registers with the raised pattern in the back-up or impression
roller.
FIG. 8 is a plan view of a portion of the surface of a patterned
gravure roller as in FIG. 7.
FIG. 9 is a plan view of a portion of the surface of another
patterned gravure roller having etched cells defining the
pattern.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to the drawings, a schematic view of apparatus for
continuously bonding and creping a web in accordance with the
invention is shown generally at 10 in FIG. 1. A roll 12 of base
substrate is unrolled and the web passed into a nip formed between
a gravure roller 14 and a back-up or impression roller 15. The base
substrate material from the roll 12 is preferably a high
absorbency, low density web having low internal fiber bonding. Such
webs can be produced by various conventional processes, such as
through-air-drying, air laying, and other processes which produce
products having similar characteristics. The present process has
the singular advantage of producing a web which retains a
substantial portion of the bulk and absorbency of such initial base
substrates. In general, it is preferred that the starting webs have
very little internal cohesion, and commensurate high bulk and
absorbency, since the product formed in accordance with the present
process adds sufficient tensile strength to yield a satisfactory
product.
The gravure roller 14 of FIG. 1 has a surface which is engraved
with lines and which picks up the binding liquid from a pan 18 and
delivers it to one surface of the web. A doctor blade 20 is used in
the customary fashion to remove excess liquid from the surface of
the gravure roller.
After having the binding liquid applied to one surface, the bonded
web 21 is passed around a pressure roller 22 and into contact with
the polished, heated surface 24 of a drying/creping cylinder 25. As
the moistened web drys on the cylinder surface, it develops
adhesion thereto, which allows the web to be creped from the
cylinder surface by a creping blade 27. The creped web 28 may then
be rewound for further processing, or, as shown in FIG. 1, the web
may be passed around support rollers 29 and 30 and thence into a
nip formed between a second gravure roller 32 and a second
impression roller 33. The gravure roller 32 receives binding liquid
from a pan 34, has its surface wiped by a doctor blade 35, and
delivers the binding liquid into contact with the side 37 of the
web 28 which is opposite to the side which had previously received
a coating of creping liquid. The wetted web is then passed around
support rollers 38 and 39 to a pressure roller 40 which applies the
web, moistened side down, against the surface 42 of a second
drying/creping cylinder 43. The dried web is creped from the
surface of the cylinder 43 by a creping blade 44, is passed through
the nip formed between two calender rollers 45 and 46, which
lightly press the creped web, is thence passed through a curing
station 48 which applies heat to the web to heat cure and
cross-link the binder material, and is wound up onto a roll 50 to
await further processing.
The impression roller 15 is shown in more detail in the view of
FIG. 2. This roller has a central metal core 52 with a resilient
rubber sheet or blanket 53 mounted on its surface. The resilient
sheet is formed with raised surface areas 54 forming linear bands
which interconnect with each other and define a rectilinear network
which surrounds and separates depressed areas 55 on the impression
roll surface. The height of the raised areas 54 above the depressed
areas 55 is preferably selected to be greater than the uncompressed
thickness of the starting web 12. It should be understood that the
dimensions of the spacing between the raised areas 54 relative to
the overall size of the roller 15 is shown greatly exaggerated in
FIG. 2 for purposes of illustration. In practice, the width of the
depressed areas 55 would be in the range of 3 to 12 millimeters and
the width of the raised surface bands 54 would be approximately 0.5
to 1.5 millimeters.
A side view of the nip between the gravure roller 14 and the
back-up roller 15 is shown in greater detail in FIG. 5. As
illustrated therein, the raised areas 54 press the underlying
portions of the web 12 firmly against the surface of the gravure
roller 14. At these areas of firm pressing 57 there is substantial
pick up of binding liquid from the gravure roller which migrates
substantially through the web 12 toward the raised surfaces 54.
Preferably, however, the pressure applied by the impression roller
is adjusted to suit the rheology of the binding liquid so that the
liquid does not pass all the way through the web and accumulate on
the raised surfaces 54. The gravure roller surface illustrated in
FIG. 5 has a multitude of depressions such as engraved lines or
cells uniformly distributed over the surface of the roller which
act as reservoirs for binding liquid; thus, a greater quantity of
liquid per unit area will be absorbed by those areas 57 of the web
that are firmly pressed against the gravure roller surface than
will be absorbed by areas of the web that are only lightly pressed.
The combination of fiber compaction and heavy pick-up of binding
liquid causes the areas 57 to be areas of high strength and high
density. The areas 57 have the same general pattern as the raised
areas 54 on the impression roller--that is, an interconnected
rectilinear network spreading throughout the web. In between the
densified areas 57 are larger areas 58 which underlie the depressed
areas 55 in the impression roller and therefore retain a
substantially uncompressed and bulky cross-section, as illustrated
in FIG. 6. After curing of the binding liquid, the densified areas
57 provide a two-dimensional network of lines of strength extending
throughout the web which gives the web the desired tensile strength
in both the machine and cross directions.
The impression roller 33 and gravure roller 32 are preferably
constructed identically to and function in a similar manner to the
impression roller 15 and gravure roller 14, respectively. The only
difference in function and result between the respective rollers is
that the gravure roller 32 applies a coating of binding liquid to
the side of the web which is opposite to the side which had binding
liquid applied to it by the gravure roller 14. In addition, the
raised areas on the impression roller 33 almost certainly will not
coincide with the densified areas 57 produced by the first
impression roller 15. Rather, the raised areas on the impression
roller 33 may be expected to be in random alignment with regard to
the densified areas 57 and the bulked areas 58, so that a second
network of densified areas will be formed in the web which
partially overlaps the original densified areas 57 and also
partially overlaps, and thereby densifies, portions of the original
bulked up areas 58. The resulting cured web will thus have at least
two super-imposed networks of lines of strength with, however,
bulked up areas remaining between them.
The creping of the web on the creping cylinders 25 and 43 serves to
partially restore some of the bulk and softness which are lost when
the binding liquid is applied to the web, and particularly bulks up
and separates the fibers in those portions of the web which have
not been densified by pressing.
A pressure roller, such as the roller 22, is conventionally used to
press a web against the surface of the drier cylinder to cause
proper adhesion. A plain pressure roller 22 having a soft,
resilient surface may be utilized to press the web against the
surface, but it is preferable in the present process that the
pressure be minimized so that there is not firm overall compaction
of the fibers of the web at the nip formed between the pressure
roller and the drier surface. The web may alternatively be laid
upon the drier surface without the use of direct contact by a
pressure roller, in the manner shown in the Klowak, et al. patent,
U.S. Pat. No. 4,125,659. In a preferred embodiment of the present
invention, the pressure roller 22 also is formed with raised
pattern surfaces defining an interconnected network surrounding
depressed areas, with the raised portions being higher than the
thickness of the web. The pressure roller 40 is also preferably
formed in this manner.
In contrast to the effect on the web resulting from the pressure
applied by the raised areas of the pattern rollers 15 and 33, the
pressure applied on the web by the raised areas on the pressure
rollers 22 and 40 does not cause an increase in pickup of binding
liquid, although the portions of the web being compressed may show
a slight increase in the relative migration of binding liquid from
the surface of the web to the interior fibers. However, the amount
of binding liquid which can migrate into the web will be relatively
small since the areas 58 which have not been compressed against the
gravure roller will have picked up only a very light coating of
binding liquid.
Some additional densification of the web will take place under the
raised pattern in the pressure rollers because the pattern on these
rollers will not necessarily coincide with the densified areas 57
produced at the nip between the impression roller and the gravure
roller. The amount of overlap between the raised areas on the
pressure rollers and the raised areas on the impression rollers may
be expected to be random, so that a portion of the areas left
uncompressed by the impression roller, such as the areas 58 shown
in FIG. 6, will be compressed and thus strengthened. However, there
will still remain areas within the web which are not compressed at
all.
The main effect of the patterned pressure roller 22 (and similarly,
of the patterned pressure roller 40) is to provide areas of strong
and weak adhesion of the web to the surface of the drier cylinder,
which areas correspond, respectively, to those portions of the web
which are pressed by the raised pattern on the pressure roller and
those portions of the web which are not so pressed. The pattern
differential in pressure results, after creping of the web by the
creping blade 27, in a web which has a superimposed creping pattern
in it, concentrated in the side of the web facing the drier
surface, corresponding to the pattern of the pressure roller 22. As
described in the aforesaid patent U.S. Pat. No. 4,125,659, the
pattern in the creped web comprises alternating areas of very fine,
dense crepes corresponding to the high adhesion areas of the web
and areas of broad, widely spaced crepes corresponding to the low
adhesion areas of the web. A similar patterned creping action,
concentrated on the opposite side of the web, occurs at the drier
cylinder 43 as the web is creped off by the creping blade 44.
An additional creping pattern is formed in the web because of the
concentration of binding liquid in the compressed areas of the web.
The areas of higher concentration of binding liquid/creping
adhesive are more strongly adhered to the creping surface and a
finer crepe occurs in these areas.
The result of these several operations is a very complex multiple
layer paper web. The product has superimposed rectilinear networks
corresponding to the compression patterns provided by the
impression rollers 15 and 33, in which the fibers of the web are
firmly compressed and binding liquid has been dispersed into the
web to bond the two layers together. The densest areas of the web
are those which have been pressed by the impression rollers 15 and
33 and by the pressure roller 22 and/or by the pressure roller 40;
these areas also show a fine crepe resulting from the higher
concentration of binding liquid therein. Areas of intermediate
density and creping exist at those portions of the web which have
been pressed only by the impression roller 15 and/or the impression
roller 33. There are also superimposed areas of the web which have
been pressed only by the pressure rollers 22 and 40 and which
therefore have a denser crepe and somewhat greater fiber compaction
than the remaining areas of the web which have not been compressed
at all.
It will be appreciated that the various patterns formed in the
web--specifically: (1) the highly compressed, highly bonded, finely
creped rectilinear network corresponding to the pattern on the
impression roller 15, (2) the highly compressed, highly bonded,
finely creped rectilinear network corresponding to the pattern on
the impression roller 33, (3) the densely creped rectilinear
network corresponding to the pattern on the pressure roller 22, and
(4) the densely creped network corresponding to the pattern on the
pressure roller 40--will all overlap one another in a random
manner. Based on the assumption that the relative alignment of the
raised patterned surfaces between any two of the various rollers
referred to above is an independent random variable having a
uniform probability distribution, the expected values of the
fractional areas which are subjected to various amounts of pressing
are given in the table below.
__________________________________________________________________________
Fractional Areas Subjected to: Raised Quad- Total Area - Single
Double Triple ruple Area Fraction Press Press Press Press Pressed
__________________________________________________________________________
1st F.sub.1 S.sub.1 = F.sub.1 D.sub.1 = 0 R.sub.1 = 0 Q.sub.1 = 0
T.sub.1 = F.sub.1 Pressing 2nd F.sub.2 S.sub.2 = F.sub.1 + D.sub.2
= F.sub.1 F.sub.2 R.sub.2 = 0 Q.sub.2 = 0 T.sub.2 = T.sub.1 +
Pressing F.sub.2 - 2F.sub.1 F.sub.2 F.sub.2 (1 - T.sub.1) 3rd
F.sub.3 S.sub.3 = S.sub.2 + D.sub.3 = D.sub.2 + R.sub.3 = D.sub.2
F.sub.3 Q.sub.3 = 0 T.sub.3 = T.sub.2 + Pressing F.sub.3 (1 -
S.sub.2 - T.sub.2) F.sub.3 (S.sub.2 - D.sub.2) F.sub.3 (1 -
T.sub.2) 4th F.sub.4 S.sub.4 = S.sub.3 + D.sub.4 = D.sub.3 +
R.sub.4 = R.sub.3 + Q.sub.4 = R.sub.3 F.sub.4 T.sub.4 = T.sub.3 +
Pressing F.sub.4 (1 - S.sub.3 - T.sub.3) F.sub.4 (S.sub.3 -
D.sub.3) F.sub.4 (D.sub.3 - R.sub.3) F.sub.4 (1 - T.sub.3)
__________________________________________________________________________
Thus, it is expected that some portion of the web will always
remain unpressed, even after four pressings. For example, if each
roller has a raised areas comprising 30% of its surface, the
expected area of the web pressed at least once after four pressings
will encompass 76% of the area of the web, leaving 24%
unpressed.
In addition to the various patterns that are formed in the final
product, the light, uniform coating of binding liquid applied to
each surface of the web in those areas not compacted by the raised
patterns on the impression rollers hardens, upon curing, the form a
thin layer of bonded fibers. Because the binding liquid does not
migrate into the interior of the web at these areas, the inner
fibers are loosely bonded together only by natural hydrogen
bonding, if bonded together at all. As a result, the surface of the
final product exhibits very good resistance to linting--that is, a
loss of fibers while being rubbed--but the interior of the web
still retains excellent water absorbency because the fibers in the
interior are relatively widely dispersed and allow room for
significant amounts of water to be absorbed by capillary
action.
Another embodiment of apparatus for bonding and creping webs in
accordance with the invention is shown generally at 70 in FIG. 3. A
web 71 of preferably highly bulked and debonded base substrate is
unrolled and passed into a nip formed between a gravure roller 74
and a combination impression and pressure roller 75. The web is
passed around the roller 75 and into pressure contact with the
surface 76 of a heated drier cylinder 77. Binding liquid is
supplied from a pan 79 to the surface of the gravure roller 74
which is wiped by a doctor blade 80. The gravure roller offers
binding liquid to the surface of the web which it contacts.
The drying of the binding liquid while on the surface of the heated
drier cylinder 77 causes the web to adhere thereto and allows the
web to be creped from the surface of the cylinder by a creping
blade 82. The web 83 is then passed over supporting rollers 84, 85,
and 86 to a nip formed between a second gravure roller 87 and a
second combination impression and pressure roller 88. The gravure
roller 87 picks up binding liquid from a pan 89 and has its surface
wiped by another doctor blade 90 so as to offer a surface coating
of binding liquid as it meets the side of the web 83 opposite to
the side which had binding liquid applied thereto by the gravure
roller 74. The web is passed around the roller 88 into contact with
the surface 91 of a second drier cylinder 92, to which it adheres
as the binding liquid dries, and is creped off the surface of the
drier cylinder by a creping blade 93. The resulting creped web 96
is then passed around return rollers 94 and 95 and delivered
through a heat curing station 97 to a roll (not shown) or to
subsequent converting operations.
The two sets each of gravure rollers 74 and 87, pressure/impression
rollers 75 and 88, and drier cylinders 77 and 92 function similarly
to one another, although the details of construction may be varied.
The action of these components may be illustrated with reference to
the somewhat more detailed view of FIG. 5, showing the gravure
roller 74, pressure/impression roller 75 and creping cylinder 77.
The impression roller 75 is preferably formed in a manner identical
to the impression roller 15 shown in FIG. 2, having raised areas 98
which define an interconnected rectilinear network and depressed
areas 99 which are spaced below the raised areas a distance which
is preferably greater than the uncompressed thickness of the web
71. At the nip between the rollers 74 and 75, the web 71 is pressed
firmly against the surface of the gravure roller 74 under the
raised areas 98, causing compression of the fibers and substantial
penetration of binding liquid into these fibers. The areas of the
web between those areas pressed by the raised surfaces 98 are
substantially uncompressed and, since they have only a light
contact with the surface of the gravure roller, they pick up only a
very light coating of binding liquid if the gravure roller surface
is uniformly engraved.
The resulting compression of the web is similar to that occuring at
the nip between the rollers 14 and 15, as described above, with the
exception that the web moves around the impression roller 75 such
that the compressed areas of the web remain in registry with the
raised surfaces 98 until the web contacts the surface 76 of the
drier cylinder. At this point, the once compressed areas of the web
are again pressed by the raised surface, this time against the
surface of the drying cylinder; and this second pressing results in
compaction of the web and adhesion to the drying clyinder at these
areas which is much greater than the compaction and adhesion at the
remaining areas of the web. The greater adhesion to the drier
cylinder surface occurs because of the pressure applied by the
raised surfaces against the web and because the amount of binding
liquid picked up by the web under the raised surfaces is greater
than that picked up in other areas of the web. When the web is
creped from the drier cylinder surface, it will have an
interconnected network of lines of strength therein, corresponding
to the areas compressed by the raised surfaces on the roller 75,
and, in addition, a differential crepe composed of vey fine crepes
occurring in the compressed areas and very course crepes or no
crepes at all occurring in the uncompressed areas.
When the once creped web 83 is passed through the nip between the
rollers 87 and 88 and is creped off of the drier cylinder 92, the
resulting product will show two superimposed networks of lines of
strength and two superimposed patterns of differential creping
coinciding with the lines of strength in the web, with fine crepes
occurring at or adjacent to the lines of strength in the web and
course crepes or no crepes at all occurring in the uncompressed
areas between the lines of strength. The position of the
impressions applied by the roller 75 into the web will generally
not coincide with the impressions applied by the roller 88--the
position of the paper web with respect to the patterns on these
rollers cannot be practicably synchronized even if desired--so that
the two superimposed networks of compressed areas will be randomly
aligned.
Another apparatus for producing bonded and creped webs in
accordance with the invention is shown generally at 101 in FIG. 6.
In this apparatus, the base web 102 is unwound from a roll and
passed through a nip between an impression roller 105 and a gravure
roller 106 which picks up binding liquid 107 from a pan 108 and has
its surface wiped by a doctor blade 109. The resulting web 110 is
dried without pressing, preferably by being passed through a
flotation drier 111 in which heated air thoroughly dries the
binding liquid in the web. Alternatively, the web could be dried by
applying it to a drier cylinder without the use of a pressure
roller. The dry web from the flotation drier moves over support
rollers 113, 114, 115, and 116 to a nip formed between a second
impression roller 118 and a second gravure roller 119. The gravure
roller picks up binding liquid 120 from a pan 121 and is wiped by a
doctor blade 122 so that a layer of binding liquid is left on the
gravure roller surface. After pick up of binding liquid, the web
moves to a nip between a pressure roller 124 and a second drier
cylinder 125 which is heated to dry the web and allow it to be
creped from the drier surface by a creping blade 126. The creped
web is then passed through a curing station 127 to set the binding
liquid and render it water insoluble, and the resulting web is
thence transferred to a roll (not shown) or to other converting
operations.
The impression rollers 105 and 118, and the pressure roller 124 are
preferably formed identically to the roller 15 shown in FIG. 2.
Thus, the roller 105 presses into the web an interconnected
rectilinear network of compressed areas which have substantial
amounts of binding liquid absorbed into them, while leaving the
areas between the compressed areas substantially uncompressed and
with only a light coating of binding liquid thereon if the surface
of the gravure roller 106 is uniformly etched or engraved. No
differential crepe is formed in the web as a result of the
application of binding liquid by the combination of the gravure
roller 106 and the impression roller 105.
A similar and superimposed interconnected rectilinear network of
compressed areas is formed in the web by the action of the
impression roller 118 against the surface of the gravure roller
119. In addition, the liquid picked up by the web from the gravure
roller under the raised areas of the impression roller 118 results
in a finer crepe at the pressed areas of the web when the web is
creped off of the drier cylinder 125. The pressure roller 124 may
be a patterned roller, in which case it will impress a pattern of
interconnected grid lines into the web which will cause the areas
of the web so compressed to be more tightly adhered to the surface
of the drier than those areas which are not compressed. The
resulting creped web has a denser and finer crepe at those areas
which are pressed by the pressure roller 124 than at those areas
which are not pressed. This differential creping pattern will be
superimposed upon that caused by the differential in binding liquid
pickup achieved at the nip between the rollers 118 and 119.
Alternatively, the pressure roller 124 may be a smooth surfaced
roller which applies only light, but uniform contact of the web to
the drier surface, and therefore no differential crepe results from
this pressure, although the web will still exhibit a differential
crepe resulting from the patterned application of binding
liquid.
The above described processes and the apparatus for carrying them
out are particularly adapted to produce a highly desirable product
from a base substrate which has very low internal cohesion and very
high initial bulkiness and water absorbency. For the most part, the
generalization can be made that the lower the density and tensile
strength of the initial base substrate webs, the better will be the
bulk and absorbency of the final product. The webs produced in
accordance with the invention have the necessary tensile strength
and surface cohesion added to them by the application of binding
liquids in the manner described above. To achieve the tensile
strength required, it is essential that the pattern of binding
liquid and densified fibers within the web be an interconnected
lattice or network so that substantially uniform and adequate
tensile strength is obtained within the finished product in the
plane of the web. Thus, at least one, and preferably both of the
impression rollers (or one and preferably both of the combined
impression/pressure rollers) will have raised areas on their
surfaces defining an interconnected network. These raised areas may
define the geometric pattern shown in somewhat simplified form in
FIG. 2, or they may be other geometric patterns which nonetheless
provide an interconnected network, such as are shown in the
aforementioned patent U.S. Pat. No. 4,125,659.
It is not necessary that the pressure rollers, which only function
to press the web against the surface of the drier cylinders, have
raised areas defining an interconnected network, although they may
certainly have such raised areas if desired. As described above,
these pressure rollers may simply be smooth surfaced rollers
providing light contact, or they may have raised areas defining
patterns which are not interconnected. The use of the latter type
of pattern on the pressure roller will result in a pattern crepe in
the final product defined by denser and finer crepes in the areas
that were pressed by the raised areas of the pressure roller and
coarser crepes or no crepes at all in those areas which were not so
pressed. Thus, a variety of superimposed and aesthetically
interesting creping patterns can be formed in the final product by
the selection of the various surface patterns on the impression
rollers and the pressure rollers.
Generally, the diamond-shaped raised patterns illustrated in FIG. 2
are preferred for use on the impression or impression/pressure
rollers. Satisfactory results are obtained where the raised areas
constitute 20% to 40% of the total area of the roller, with
exemplary quadrangular shaped cells having their widest angles
varying from 90.degree. to 140.degree., and with the spacing
between raised areas being approximately 3 to 12 mm.
As an alternative to utilizing a uniform surfaced gravure roller
which carries binding liquid over its entire surface, the gravure
roller may have depressions which carry the binding liquid in a
pattern. An example is shown in FIG. 7, in which the gravure roller
130 has grooves 131 which underlie the raised areas 54 on the
impression roller 15. The surfaces areas 132 of the roller 15
between the grooves 131 are smooth and polished. The rollers 14 and
15 are mechanically driven together, such as with gearing (not
shown), so that the raised areas 54 and the grooves 131 always
remain in registry.
A portion of the surface of the gravure roller 130 is shown in FIG.
8. Preferably, the width of the raised areas 54 is slightly greater
than the width of the etched grooves 131, so that the edges of the
raised areas 54 lie over the smooth surface areas 132 of the
gravure roller 130. The position at which the edges of the raised
areas 54 meet the smooth areas 132 is illustrated by the dashed
lines labeled 134 in FIG. 8. For example, with an impression roller
having a 90.degree. diamond pattern of raised areas defining
squares 5.44 mm on a side, 0.762 raised area width, a satisfactory
width for the etched grooves 131 is 0.635 mm. Typically, the
grooves would be depressed approximately 0.0635 mm from the
surface.
The binder liquid applying areas 131 of the gravure roller may also
be formed as discrete etched cells, rather than grooves, as shown
in FIG. 9.
By utilizing a patterned gravure roller with the liquid applying
areas 131 having a pattern matching and registering with the
pattern of raised areas 54, the binding liquid is applied to the
web only in a rectilinear pattern of compressed areas having
binding liquid therein. The areas of the web between the
rectilinear pattern are uncompressed and free of binding liquid,
thus retaining maximum softness and absorbency.
It may be noted that the patterned gravure roller as described
immediately above may be used to apply binding liquid in any of the
embodiments of the invention shown in FIGS. 1, 3 and 6.
The binding liquid utilized in the process of the invention must
possess several qualities: it must be capable of providing adequate
tensile strength in the finished product after curing, readily
penetrating the fibers of the web so that bonding between plies
takes place, and quickly drying and adhering the web to the creping
cylinders for proper creping. Where a product having wet strength
is desired, the binding liquid must also be capable of being cured
to a water insoluble state. A preferred composition of the binding
liquid is illustrated with reference to the example below.
The initial substrate web provided for creping was formed by a
modified conventional wet press papermaking process and had a basis
weight of 38 pounds per ream (3,000 sq. ft.), a machine direction
tensile strength of 58 grams per centimeter, a cross direction
tensile strength of 28 grams per centimeter, and a caliper for 8
plies of 2.27 mm under a compressive load of 26.6 g/cm.sup.2. The
binding liquid applied to the web comprised, as a percentage of the
total weight of the binding liquid: 22.59% ethylene vinyl acetate
(A-120 Latex, 52% solids), 2.26% acrylic polymer (B-85 Latex, 38%
solids), 1.3% polyvinyl alcohol (12% solids), to act as a thickner
and generally improve rheology; 0.12% colloids (581-B) and 0.06%
tri-n-butyl phosphate to act as defoaming agents; 0.68% Cymel 303
to act as a cross-linking agent, 0.23% NaHSO.sup.4, to act as a
catalyst to increase cross-linking, and 72.70% water. The viscosity
of the binding liquid as measured by a Brookfield RVF 100
Viscosimeter was 680 cps. at 21.degree. C. and pH 5.7.
The binding liquid was applied to one side of the substrate web
using a uniform surfaced 110 lines per inch gravure roller having
quadrangular knurled cells about 0.0037 inch (0.09398 mm) deep. An
impression roller was used having 35.7% raised surface area
defining a 90.degree. diamond pattern of cells having 0.214 inch
(5.44 mm) cross direction length and 0.03 inch (0.762 mm) raised
surface band width. The web was fed through the gravure-impression
roll nip which was set for approximately 0.002 inch (0.0508 mm)
clearance, and binding liquid add on to the web was found to be in
the range of 3.5% or about 1 pound per ream. Due to wetting of the
substrate at the gravure roller, a speed differential equivalent to
8% existed between the speed of the roller at the gravure nip (74
feet per minute) and the speed of the surface of the heated creping
cylinder (80 feet per minute). After application of the binding
liquid, the web comprised 86.9% oven dried solids.
A ripple patterned pressure roll, as described in the Klowak, et
al. patent, U.S. Pat. No. 4,125,659, was used to press the web to
the creping cylinder at a pressure loading of 40 pounds per linear
inch at the nip between the pressure roller and the cylinder
surface, which was heated to 225.degree. F. The pressure roller was
covered with a rubber sheet having the ripple pattern with its
raised surfaces covering 55% of the total area of the roller.
After adherence to the creping cylinder and substantial drying, the
web was creped from the cylinder surface with a creping blade to
increase its bulk, softness and absorbency. The web was rewound
before being passed a second time through the same apparatus,
rather than being directly passed another gravure station as shown
in FIG. 1. Therefore, the crepe imparted from the first pass was
pulled out of the product at the wind-up roll to reduce the basis
weight and bulk, thereby helping to decrease the amount of binding
liquid added to the product in the second pass through. The creping
remaining in the product this time was 4%, resulting from a speed
differential of 80 feet per minute at the creping cylinder surface
and 77 feet per minute at the wind-up roll.
The second pass through the apparatus was under essentially
identical conditions as in the first pass but with the previously
untreated side of the web in contact with the gravure roller and
the binding liquid. The speed differential between the gravure and
impression rollers (78 feet per minute) and the creping cylinder
(83 feet per minute) resulted in a web speed change of
approximately 6% to account for wetting of the web. The amount of
binding liquid added onto the web was 4.2% on a dry weight basis or
1.2 pounds per ream, which wetted the entire web to 85.0% oven
dried solids. To maximize bulk and associated water holding
capacity, the web was creped from the creping drum at a 4% crepe,
obtained with a speed at the drum surface of 83 feet per minute and
at the wind-up of 80 feet per minute. The product was then placed
in an oven for curing at 300.degree. F. for 3 minutes.
The resulting product had a basis weight of 33.4 pounds per ream, a
caliper for 8 sheets of 0.152 inch (3.87 mm) under a compression
load of 26.6 g/cm.sup.2, a dry geometric mean tensile strength of
126 grams per centimeter, a dry tensile ratio of 1.4, a wet cross
direction tensile strength of 83 grams per centimeter, a water
holding capacity total of 665 grams per square meter, and a water
holding capacity ratio of 12.7.
The water holding capacity test utilized to measure the
characteristics of the product is the test developed by J. A. Van
den Akker which has been submitted for certification to the
American Society for Testing Materials. This test may be briefly
summarized as follows. At least five specimens, three inches by
three inches on a side, are cut from the finished web. Each
specimen is weighed and the weight recorded by itself and while on
a metal specimen catcher plate. Each specimen is then laid upon
back-up foamed plastic with the side to be laid in contact with the
water facing up, and a row of hooks on a specimen holder is pushed
through the specimen as it is supported on the foamed plastic. The
specimen holder and specimen are then inverted and the specimen is
laid on water held in a dish. A stop watch is started at the moment
that the specimen contacts the water. After 59 seconds, the
specimen is lifted from the water and laid on an excess water
extractor formed of an aluminum plate with a series of slots milled
in it to allow excess water to drain out. The elevation of the top
surface of the excess water extractor above the pool of water is
maintained at 5 mm, so that the specimen is subjected to a suction
head of 5 mm of water. The specimen is left on the excess water
extractor plate for 15 seconds, is then lifted and placed on the
specimen catcher, the specimen holder is removed, and the
combination of the specimen catcher and wet specimen is weighed and
the weight recorded. The other specimens are tested in the same
manner and another series of specimens may be tested to determine
the water holding capacity of the other side of the web. The dry
and wet specimen weights in grams are calculated by subtracting the
known weight of the specimen catcher from the combined weights,
calculating the dry basis weight of the specimens in grams per
square meter, and calculating the amount of water held by the
specimen, in grams, by subtracting the dry specimen weight from the
wet specimen weight. The total water holding capacity is then
calculated as the number of grams of water held per square meter by
multiplying the water held by the specimen by 172. The water/fiber
ratio or water holding capacity ratio is calculated by taking the
ratio of the weight of the total water held to the dry specimen
weight.
The resulting water holding capacity ratios for products formed in
accordance with the present invention, as indicated in the example
above, compare favorably with products formed by more expensive air
laying and through-air-drying processes, which typically have water
holding capacity ratios in the range of 13 to 17. In addition, the
present product may have a uniform although light coating of wet
strength bonding material on both of its surfaces, thereby making
the product resistant to linting of fibers from the surface, a
common problem with paper products which have had internal bonding
between fibers decreased so as to increase the water holding
capacity.
It is understood that the invention is not confined to the
particular embodiments disclosed herein as illustrated, but
embraces such modified forms thereof as come within the scope of
the following claims.
* * * * *